Field of the Invention
The invention relates to an optical device having a plurality of optical elements disposed laterally adjacent to one another. Each of the optical elements being assigned an optical axis and has a light entry surface and a light exit surface.
In lighting systems based on light emitting diodes (LEDs), lenses are normally used to collimate the radiation emitted. For efficient illumination in this case, a large entry aperture or a high luminous intensity of the collimating optics is desirable.
A high luminous intensity can generally be achieved by short focal length lenses of large diameter. Disadvantageously, this also entails a large lens thickness, which leads to heavy, large volume illumination systems requiring a great deal of material. In the case of spherical lenses, a further drawback resides in the fact that the projection errors increase with increasing distance from the optical axis. In addition, the reflection losses increase toward the edge of the lens, because of the entry angle becoming flatter.
In the case of lighting systems with a plurality of individual LEDs as a light source, the aforementioned projection errors and shadows in the edge regions of the individual collimating lenses lead to an inhomogeneous luminous flux distribution. In particular, the individual light sources often remain detectable, which is undesirable in the signaling and lighting sectors.
One improvement is achieved by Fresnel stepped lenses, as they are known, as disclosed by International Patent Disclosure WO 87/00297, for example. In the case of these stepped lenses, the lens surface is subdivided in the manner of steps into a large number of annular, concentric zones, so that a flatter configuration that saves material is achieved. Nevertheless, these lenses also exhibit considerable shadows at a relatively large distance from the optical axis. Furthermore, the overall transmission of such lenses is limited by the large number of discontinuities and edges on the lens surface.